1. Field of the Invention
The present invention relates to a magnetic sensing element mounted on, for example, a hard disk device or the like, and particularly to a magnetic sensing element having no variation in the track width and capable of appropriately complying with track narrowing.
2. Description of the Related Art
FIG. 21 is a partial sectional view of a conventional sensing element (spin-valve thin film element), as viewed from a surface facing a recording medium.
Reference numeral 1 denotes an underlying layer made of Ta or the like. An antiferromagnetic layer 2 made of a PtMn alloy or the like, a pinned magnetic layer 3 made of a NiFe alloy or the like, a nonmagnetic intermediate layer 4 made of Cu or the like, a free magnetic layer 5 made of a NiFe alloy or the like, a protecting layer 6 made of Ta or the like are formed on the underlying layer 1. The layers ranging from the underlying layer 1 to the protecting layer 6 constitute a magnetoresistive film 9.
In the conventional example shown in FIG. 21, hard bias layers 7 made of a hard magnetic material are formed on both sides of the magnetoresistive film 9 in the track width direction (the X direction shown in the drawing), and electrode layers 8 are respectively formed on the hard bias layers 7.
However, the spin-valve thin film element shown in FIG. 21 has the following problem.
Although the width dimension of the upper surface of the free magnetic layer 5 in the track width direction is defined as track width Tw, the track width Tw will be decreased with increases in the recording density in future. In this case, both side ends 5a of the free magnetic layer 5 are magnetized by strong longitudinal bias magnetic fields from the hard bias layers 7 to cause difficulties in reversal of magnetization at both side ends 5a with an external magnetic field. This causes so-called dead zones. Therefore, a zone (a so-called sensitive zone) which can produce substantial reversal of magnetization, and exhibit magnetoresistance becomes narrower than the track width Tw, thereby causing the problem of further narrowing the sensitive zone to decrease reproduced output with track narrowing.
Therefore, a conventional spin valve thin film element has a structure improved for securing a sensitive zone of a predetermined size even if both side ends 5a of the free magnetic layer 5 become the dead zones, as described below.
FIG. 22 is a partial sectional view of an improved conventional spin valve thin film element, as viewed from the surface side facing a recording medium. In the drawing, the layers denoted by the same reference numerals as FIG. 21 denote the same layers as FIG. 21.
In the conventional example shown in FIG. 22, the width dimension of the upper surface of the free magnetic layer 5 in the track width direction is T1 longer than the track width Tw shown in FIG. 21.
The electrode layers 8 are formed to extend from the hard bias layers 7 to the protecting layer 6 formed on the free magnetic layer 5. The portions of the free magnetic layer 5, which are overlapped with the electrode layers 8, are the dead zones.
In this conventional example, the track width Tw is defined by the space between the electrode layers 8, and the area in the track width Tw corresponds to the sensitive zone of the free magnetic layer 5. Therefore, the whole area in the track width Tw is substantially concerned with magnetoresistance.
In the conventional example, the width dimension T1 of the free magnetic layer 5 in the track width direction can be appropriately regulated to secure the sensitive zone of a predetermined size even in narrowing of the track in future, and thus a predetermined level of reproduced output can be expected.
FIG. 23 shows the structure of the magnetic sensing element shown in FIG. 22, as viewed from above.
As shown in a partial plan view of FIG. 23, the electrode layers 8 are formed to overlap the upper surfaces of the hard bias layers 7 formed on both sides of the magnetoresistive film 9 in the track width direction so that the inner side ends 8a of the electrode layers 8 are overlapped with both side ends 5a of the free magnetic layer 5.
FIGS. 24 to 27 respectively show the steps of manufacturing the magnetic sensing element shown in FIGS. 22 and 23. FIGS. 24A to 27A are partial plan views, and FIGS. 24B to 27B are partial sectional views taken along one-dot chain lines in FIGS. 24A to 27A, respectively, as viewed from the direction of arrows.
In the step shown in FIG. 24, after the magnetoresistive film 9 is deposited on a substrate 10, a resist layer 12 is formed on the magnetoresistive film 9, and a pattern 12a for forming biases and electrodes in the resist layer 12 is formed by an exposure phenomenon. Then, the portions of the magnetoresistive film 9, which are exposed from the pattern 12a, are moved by ion milling or the like, and the hard bias layers 7 are then deposited by sputtering substantially perpendicularly to the substrate 10.
Next, in the step shown in FIG. 25, the electrode layers 8 are formed to overlap the hard bias layers 7 by using the resist layer 12. In this step, the sputtering angle is set so that the sputtering direction is more inclined than that in the formation of the hard bias layers 7, thereby permitting the formation of the electrode layers 8 in notch portions formed at the lower surface of the resist layer 12. Consequently, the inner side ends 8a of the electrode layers 8 can be formed to overlap both side ends 5a of the free magnetic layer 5. Then, the resist layer 12 is removed.
In the step shown in FIG. 26, a resist layer 11 for determining the rear end in the height direction is formed on the electrode layers 8 and the magnetoresistive film 9 held between the inner side ends 8a of the electrode layers 8. Then, the portions of the electrode layers 8 and the magnetoresistive film 9, which are not covered with the resist layer 11, are removed by, for example, ion milling in the directions of arrows F. This state is shown in FIG. 27. In FIG. 27, for the sake of ease of seeing, the portions of the hard bias layers 7, which are exposed by removing the electrode layers 8, are shaded.
As shown in FIG. 27, the resist layer 11 functions as a mask for ion milling to leave the electrode layers 8 having the same size as the resist layer 11 below the resist layer 11, and leave the hard bias layers 7 having an area larger than the lower surfaces of the electrode layers 8 below the electrode layers.
Then, the resist layer 11 is removed, and the magnetic sensing element shown in FIG. 27 is cut up to line A—A for determining the height to complete the magnetic sensing element shown in a lower drawing (partial sectional view) of FIG. 27 and FIGS. 22 and 23.
As shown in the steps shown in FIGS. 24 and 25, conventionally, the hard bias layers 7 and the electrode layers 8 are continuously formed by sputtering deposition using the same resist layer 12. However, the magnetic sensing element manufactured by the above-described manufacturing method causes the following problems.
Since a sensing current from the electrode layers 8 is liable to flow through the shortest distance, the flow of the sensing current is concentrated in the vicinity of the inner side end face 8b of each of the electrode layers 8 as shown by an arrow in FIG. 23.
However, as shown in FIG. 23, the hard bias layers 7 are present below the inner side end faces 8b of the electrode layers 8, and thus the sensing current shunts to the hard bias layer 7 provided below each of the electrode layers 8 as shown by arrow B in FIG. 22 before the sensing current passes through the vicinity of the inner side end face 8b of each of the electrode layers 8 and reaches the inner side end 8a. This causes the problem of deteriorating the current density at the inner side end 8a of each of the electrode layers 8.
Therefore, reproduced output deteriorates, and the sensing current shunting to the hard bias layers 7 also flows into the dead zones of the magnetoresistive film 9. In the dead zones, magnetization is not securely pinned, and particularly, magnetization in the areas near the dead zones is actually reversed with an external magnetic field in spite of lower sensitivity than the active zone. Therefore, the dead zones also partially function as reproducing regions to widen the track width, thereby failing to comply with track narrowing. There is also the problem of causing variations in the track width.